1. Technical Field
A method for forming a dielectric layer of a capacitor in a semiconductor device is disclosed. More particularly, a method for forming a Ta2O5 dielectric layer using a plasma enhanced atomic layer deposition is disclosed.
2. Description of the Related Art
As the level of integration increases in semiconductor devices like DRAMs (Dynamic Random Access Memory), superior electrical properties, such as high charge capacity in a limited space and reduced leakage current are needed in a DRAM capacitor. For this reason, a Ta2O5 dielectric layer, which is a high dielectric layer, is used for the dielectric layer of the capacitor.
Meanwhile, in case of a Ta2O5 dielectric layer deposited by the LPCVD (Low Pressure Chemical Vapor Deposition) method, the electric property of a capacitor deteriorates because of inferior step coverage.
To solve this problem, the atomic layer deposition (ALD) is used to improve the step coverage by repeatedly depositing a plurality of atomic layers.
FIGS. 1A to 1D are cross-sectional views illustrating the conventional method for forming a Ta2O5 dielectric layer.
First, as shown in FIG. 1A, after a polysilicon layer 11 to form a bottom electrode is deposited on a substrate 10 on which transistors and plugs are formed, the native oxide layer (now shown) on the surface of the polysilicon layer 11 is removed with HF or BOE (Buffer Oxide Etchant), and then the surface of the polysilicon layer 11 is subject to the RTP (Rapid Thermal Process) in the atmosphere of NH3.
Subsequently, as illustrated in FIG. 1B, a Ta2O5 dielectric layer 12A is deposited on the layer 11 by performing the atomic layer deposition (ALD) and the in-situ treatment of oxygen (O2) plasma.
Repeating these two procedures results in the depositing of a plurality of Ta2O5 dielectric mono layers (121xcx9c12n) which produces a Ta2O5 dielectric layer 12A with superior step coverage.
As illustrated in FIG. 1C, the process of oxygen (O2) plasma treatment is for thermally treating the Ta2O5 dielectric layer 12A in the oxygen atmosphere. This way, a crystallized Ta2O5 dielectric layer 12 is formed.
Then, as depicted in FIG. 1D, a capacitor in a stacked structure of a polysilicon layer 11, Ta2O5 dielectric layer 12 and top electrode 13 is formed by depositing a top electrode 13 on the Ta2O5 dielectric layer 12.
The conventional method for forming a Ta2O5 dielectric layer using the atomic layer deposition (ALD) and oxygen plasma described above has following problems.
First, the poor reactivity of oxygen makes carbon A remain in the Ta2O5 dielectric layer 12. Secondly, the weak activation energy of the oxygen still makes oxygen vacancy in the Ta2O5 dielectric layer 12, causing its electric property deteriorated by leakage current.
A method for forming a Ta2O5 dielectric layer using a plasma enhanced atomic layer deposition that can improve the quality of a layer and its electrical properties is disclosed.
More specifically, a method for forming a Ta2O5 dielectric layer using plasma enhanced atomic layer deposition is disclosed that comprises: a) flowing Ta(OC2H5)5 source gas in a chamber and generating plasma; b) depositing a Ta2O5 layer by using the plasma; c) purging the chamber; d)repeatedly performing the steps a) to c) in order to form a Ta2O5 dielectric layer; e) thermally treating the surface of the Ta2O5 dielectric layer in an oxygen atmosphere; and f) crystallizing the Ta2O5 dielectric layer.